Ergonomic, split and other weird keyboards
Posts must be of/about keyboards that have a clear delineation between the left and right halves of the keyboard, column stagger, or both. This includes one-handed (one half doesn't exist, what clearer delineation is that!?)
i.e. no regular non-split¹ row-stagger and no non-split¹ ortholinear²
¹ split meaning a separation of the halves, whether fixed in place or entirely separate, both are fine.
² ortholinear meaning keys layed out in a grid
No excessive posting/"shilling" for commercial purposes. Vendors are permitted to promote their products/services but keep it to a minimum and use the [vendor] flair. Posts that appear to be marketing without being transparent about it will be removed.
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Proper split ergo keyboards are pricey, and selection is very small: https://kinesis-ergo.com/keyboards/advantage360/#buy-now
I'm currently building my own Redox because I can't justify spending that much on a Kinesis: https://shop.beekeeb.com/product/redox-v1-pcb-kit/
Maybe you can get somebody to build you a Redox for less than $350? Check Etsy, ebay.
Check out Keebmaker.com. They’re US based.
I think the 2.4ghz is going to be the most rare feature. I found essentially one Etsy seller (https://www.ebay.com/sch/i.html?sid=vooooodooooo&_pgn=1&isRefine=true&_trksid=p2349624.m3561.l49496) and then the dygma. I think since Bluetooth in integrated in to microcontrollers, this becomes the simpler solution.
ErgoDox wireless from SliceMK (https://www.slicemk.com/pages/ergodox-wireless) is my suggestion. My current daily driver is a ErgoDox Wireless Lite -- been using it for about 10 months now. The guy behind it (series of wireless ErgoDox variants) is very helpful with problems on his discord. He also has a webUI configurator that works reasonably well (which I don't use because I prefer to keep my configs in git).
Not currently available, and the budget is not yet known, but it checks all your other criteria (except the travel case): https://x-bows.com/products/x-bows-split-keyboard
Otherwise, you can start with another existing option and adapt it to add what is missing. For instance, if the keyboard is built around a pro micro and you want to make it wireless, you can replace the pro micro with a nice nano and find a way to place a battery and power switch.
Leo from beekeeb offers pre-build split keyboards like this one: https://shop.beekeeb.com/product/pre-soldered-wireless-dao-choc-ble-keyboard/ and it's within your 350$ range.
It should check all your boxes except a dongle and rgb. Regarding the travel case: He even offers a soft travel pouch in the store.
RGB on a wireless split keyboard needs a pretty big battery to have more battery life than a day or too, so it's difficult to find both rgb and wireless in a pre built one without raising the costs. Also some LEDs draw constant power without even being on which also adds to this issue.